EP0433155A1 - Process for making fatigue-resistant waterproof bituminous roadsurfaces - Google Patents

Abstract

The process for making the bituminous road surface on supporting ground comprises the production of at least one base or bed course and/or a surfacing, with possible interposition of a bonding course, and it is characterised according to the invention in that a binder enrichment course of the bottom of the bed is applied onto the support before the bed course, the former comprising at least one course of aggregate and at least one course of highly over-enriched binder. Public works.

Description

The subject of the present invention is a method of building a road bituminous complex with high fatigue and impermeability capital.

The current method of building pavement reinforcement layers is almost always the same:

• 1. On applique sur le support une couche épaisse (8 à 15 cm) de matériau dit "grave bitume" et constituée d'un mélange de sable et de gravier enrobé avec 4 à 4,5% de bitume, ce bitume ayant un point de ramollissement Bille-Anneau compris entre 50 et 56°C et une pénétrabilité à l'aiguille comprise entre 35 et 50/10 mm. Préalablement à l'opération de répandage à chaud de ce mélange, on répand sur le support une fine couche de bitume de 200 à 300 g par m², appelée "couche d'accrochage", ceci afin de rendre le support suffisamment collant pour assurer la solidarisation mécanique entre la nouvelle couche et l'ancienne chaussée. La couche de grave-bitume, appelée "couche d'assise" ou couche de base, est répandue chaude et foisonnée par un finisseur puis compactée pendant qu'elle est encore chaude et donc molle et maniable.
• 2. Sur cette couche d'assise compactée et refroidie, on rajoute dans une deuxième opération une couche de roulement en enrobé dont l'épaisseur va de 4 à 8 cm, suivant les cas de trafic à supporter, cet enrobé étant, lui aussi, appliqué sur une couche d'accrochage telle qu'elle est décrite précédemment.

On an old roadway whose characteristics have become insufficient to ensure normal passage of vehicles (because the profile is deformed, because the surface is cracked by fatigue of the materials, because the thickness is not sufficient to ensure traffic during a thaw period without risking total ruin of the road), repair is carried out in two operations:

• 1. A thick layer (8 to 15 cm) of so-called "serious bitumen" material is applied to the support, consisting of a mixture of sand and gravel coated with 4 to 4.5% bitumen, this bitumen having a point Ball-Ring softening between 50 and 56 ° C and needle penetration between 35 and 50/10 mm. Prior to the hot spreading operation of this mixture, a thin layer of bitumen of 200 to 300 g per m², called "bonding layer", is spread over the support, in order to make the support sufficiently tacky to ensure the mechanical connection between the new layer and the old pavement. The layer of gravel-bitumen, called "base layer" or base layer, is spread hot and expanded by a finisher then compacted while it is still warm and therefore soft and handy.
• 2. On this compacted and cooled seat layer, a asphalt surface course is added in a second operation, the thickness of which ranges from 4 to 8 cm, depending on the traffic to be supported, this coated also being applied on a bonding layer as described above.

• - la fonction collage des couches entre elles par une couche d'accrochage bitumineuse contenant un film ténu et collant de bitume (200 à 300 g/m²), et
• - la fonction imperméabilité de la couche renforçante par la compacité de l'enrobé et de la grave-bitume, donc par la faible porosité de masse des produits constituant toutes les couches. On peut observer aussi que, pour réaliser le renforcement des anciennes chaussées, on s'en tient à l'application de deux couches de matériaux bitumineux, ces deux couches ayant toutes deux une épaisseur forte ou moyenne.

In this classic and well-known concept, we ensure:

• - the bonding function of the layers together by a bituminous bonding layer containing a thin and tacky film of bitumen (200 to 300 g / m²), and
• - The waterproofing function of the reinforcing layer by the compactness of the mix and of the bitumen, therefore by the low mass porosity of the products constituting all the layers. We can also observe that, in order to reinforce the old pavements, we stick to the application of two layers of bituminous materials, these two layers both having a strong or medium thickness.

However, we know, both in theory but also in practice, that pavements always behave better when they are highly impermeable, which on the one hand limits the profound alteration of the support soils affected by water ( and which, as a result, lose their lift) and, on the other hand, limit the frostiness of the roadways affected by the phenomenon known as thaw barriers.

On the other hand, to limit the cost of repairing pavements, it is advantageous to use materials having excellent fatigue resistance, which makes it possible to reduce the thickness of the layers, therefore the cost.

The present invention provides significant improvements in these two fields by proposing a three-layer bituminous complex with high fatigue and impermeability capital.

The subject of the invention is therefore a method of constructing a road bituminous complex on a support floor, comprising the production of at least one base or base layer and / or a wearing course, with possible interposition of a bonding layer, characterized in that an enriching layer is applied to the support, before the seat layer, by bonding from the bottom of the seat, comprising at least one layer of aggregates and at least one binder layer dosed at more than 800 g / m².

• - la couche d'enrichissement placée sous la couche d'assise et destinée à enrichir en liant la partie inférieure de cette dernière couche ― donc à la rendre encore plus résistante aux effets de fatigue en flexion. En effet, lors du compactage, l'excédent de liant remonte dans le bas de la couche d'assise. En outre, cette couche fortement dosée en liant étanchéifie particulièrement bien le sol support, par exemple l'ancienne chaussée;
• - la couche d'assise (ou de base) élaborée en grave bitume, de préférence "optimisée", afin d'être elle-même déjà très performante en fatigue;
• - la couche de surface (ou de roulement), aussi mince que possible (1 à 4 cm, et de préférence moins de 2 cm), présentant elle-même une excellente imperméabilité superficielle vis-à-vis de l'assise.

For the implementation of the invention in the general case, successively:

• - the enrichment layer placed under the seat layer and intended to enrich by binding the lower part of this last layer - therefore to make it even more resistant to the effects of fatigue in bending. In fact, during compaction, the excess binder rises at the bottom of the base layer. In addition, this highly proportioned layer of binder seals the supporting soil particularly well, for example the old pavement;
• - the base layer (or base layer) made of serious bitumen, preferably "optimized", in order to be itself already very effective in fatigue;
• - the surface layer (or surface layer), as thin as possible (1 to 4 cm, and preferably less than 2 cm), itself having excellent surface impermeability vis-à-vis the seat.

The description of the content and the role of each of these layers is given below.

The seat layer .

According to the invention, a very sophisticated seat material is used, hereinafter called "optimized" bitumen gravel, which consists of gravel, coated with a bitumen harder than that traditionally used and whose softening point Ball and Ring (standard NFT 66-008 of July 1979) is between 52 and 65 ° C, instead of 50 to 56 ° C. According to the invention, this layer is applied over 7 to 25 cm representing more than 80% of the entire thickness of the new pavement.

According to another characteristic of the invention, the bitumen dosage of the base layer is higher and between 4.5 and 5.5% by weight, instead of 4 to 4.5% in the traditional bitumen , the rest being made up of sand and gravel, each representing at least 30% by weight of the mixture (generally half / half).

These two modifications lead to a serious bitumen whose modulus (at 15 ° C, 10 Hz) is no longer from 80,000 to 93,000 bar (8,000 to 9,300 Mpa) and the fatigue strength ε6 is no longer from 90 to 100 µdef , but 95,000 to 110,000 bar (9,500 to 11,000 Mpa) with ε6 from 110 to 125 µdef.

The serious bitumen thus "optimized" is therefore already a product very resistant to fatigue.

The determination of the optimization of this serious bitumen was carried out according to the following considerations.

From an untreated gravel which has no specific modulus, we gradually pass to an increasingly bonded and cohesive material, then, when there is excess bitumen, the viscous character of the mixture reappears. In the module-bitumen content plan, we therefore go through a maximum.

To this effect of the bitumen alone, there is the effect of the compactness of the mixture which increases when the content of binder is increased.

Around this maximum, which is sought after and defined as the "optimized" low bitumen (in the stiffness sense), there is on the one hand, first the so-called enriched low bitumen (around 4.5% of bitumen), then classic bitumen gravel (around 4% of bitumen), and finally untreated gravel.

On the other side, we find the asphalt mixes (around 5.3% of bitumen) and finally the asphalt mixes around 6 to 6.5%.

We have now found that the maximum modulus (measured at 15 ° C, 10 Hz) is obtained around 5% (more exactly 5.1%) of bitumen, which of course varies with the class of bitumen used (eg 40/50 or 20/30).

If a conventional serious bitumen and an "optimized" serious bitumen according to the invention are compared to equivalent thickness, the life of the corresponding layer can be very greatly increased (factor 2 to 3).

• - de valoriser le matériau par sa durée de vie supérieure, dans le cas où les épaisseurs ne peuvent être réduites (pour des problèmes de gel par exemple), et ceci pour une augmentation de coût peu importante, et
• - de profiter de ce supplément de qualité pour diminuer (d'environ 20%) les épaisseurs des autres couches du complexe routier.

It is therefore possible, depending on the case

• to enhance the material by its longer lifespan, in the case where the thicknesses cannot be reduced (for freezing problems for example), and this for a slight increase in cost, and
• - take advantage of this quality supplement to reduce (by around 20%) the thicknesses of the other layers of the road complex.

The enrichment layer .

The purpose of this layer is to bring up an additional binder, in particular bituminous, inside the first 1 or 2 centimeters of the seat layer. This enrichment takes place during the hot application of the serious bitumen of the base which will melt the binder of the lower layer. serving as a sort of "reservoir" because it contains much more binder than is necessary. This molten binder will percolate the bottom layer from the top, during the compression under pressure of the bottom layer. In addition, this remelting of the bitumen from the enrichment layer ensures perfect bonding of the seat to the old pavement and strongly waterproofs it.

This enrichment layer consists of a reservoir coating which can be produced in the following manner.

On the old pavement (or any other supporting soil) that we want to strongly waterproof, we spread a first layer of bituminous binder (either hot melted, or in the form of bitumen emulsion), then we pour a fine layer of protective gravel with a granularity of 4/6 or 6/10 (mm).

On this first coating (called monolayer), a second identical coating is produced by spreading a layer of binder and then a layer of gravel. A coating (so-called "bilayer") is thus obtained with a double sealing layer: 2 layers of binder interposed with two layers of gravel.

It is however possible to produce this coating otherwise without departing from the scope of the invention insofar as the whole remains overdosed with binder, in particular by spreading a layer of binder between two layers of gravel (so-called sandwich coating), or by making a third coating on one or other of the systems ("three-layer" coating). Thus for n layers of binder, n or n + 1 layers of aggregates n are inserted, which can take the values 1 or 2.

According to the invention, much more binder is used than is necessary for stick the gravel and resist traffic in the known technique of surface coatings, described for example in the "Directive on the production of surface coatings" published by the Ministry of Equipment in November 1978.

On the contrary, the binder is voluntarily overdosed to produce a layer which would quickly exhibit an abundant "bleeding" of bitumen under traffic if this coating were subjected to direct traffic from vehicles. But it is this bleeding, voluntarily amplified in quantity and amplified in speed of exudation (since the serious bitumen which will overcome it will be applied hot around 150 ° C), which is precisely re-sought according to the invention to serve enrichment of the severe bitumen and provide it with additional fatigue resistance. In addition, this bitumen waterproofing layer (in particular the two-layer variant) is even safer once it has been completely remelted.

To carry out this operation, it is advantageous to use only small gravel (4/6 or 6/10) in the enrichment layer in order to facilitate the rapid exudation of the bitumen.

From the binder point of view, in particular bitumen, the total quantity spread must be greater than 800 g / m², that is to say that the excess of binder compared to a conventional coating is at least 300 g / m², and preferably between 1.2 kg / m² and 3 kg / m².

The surface or wearing course ·

It can be carried out in a known manner, but it is advantageously much thinner (1 to 4 cm) than traditional layers (4 to 8 cm).

In its thinnest version (1 to 2 cm), it can be carried out for example according to the process already described in the French patent application 89 09 893 filed on 07/21/89 by the Applicant. This technique, recently exploited under the brand EURODUIT ^R , comprises spreading a layer of binder followed by spreading a monogranular layer of praline gravel of bituminous mixture, which layer is then surfaced. This thin wearing course is applicable as soon as the evenness of the seat layer is correct, which is easily obtained on seat layers less than 9 cm thick each (when the seat layer is thick and made in several operations).

If the thickness of the seat layer is greater, its flatness is less good and it is necessary to use a slightly thicker surface layer, this to have more chances of obtaining the desired final uniform. In this case, a coating of the prior art can be applied over a thickness of 2 to 4 cm, which does not require original composition. If the total thickness of the complex is less than 10 cm, it is also possible, according to a variant, that the seat layer itself also fulfills the function of wearing course, provided that the gravel particle size is less than 14 mm.

In all cases where a wearing course is carried out independently of the seat, it is necessary to interpose a bonding layer, consisting of a bituminous binder and dosed at 250 g / m² or more, in order to improve the bonding of the wearing course and the waterproofing of the seat. According to a preferred variant, at least 400 g / m² of binder is used in order to reinforce the overall waterproofing of the complex.

The process according to the invention can be used not only for the repair of old pavements, in particular for medium traffic, but also for the construction of new pavements or mixed pavements, in particular on a foundation made of fine materials such as fly ash, sand. polluted and other poor quality materials such as chalk, possibly treated, which was practically impossible until now. It is also applicable to the coating of engineering structures.

The following examples illustrate the invention.

Example 1 :

Repair of a very damaged roadway (cracked).

a) Enrichment layer.

An enrichment layer is produced on the old pavement serving as a support by spreading twice a liter / m² of bitumen emulsion modified with latex (NEOFLEX ^R from the company SCREG), with 68% residual binder with interposition of two layers of gravel 4/6 mm. There is therefore a first sealing layer at 680 g / m² graveled in 4/6 and a second layer at 680 g / m² graveled in 4/6, ie a total of 1.36 kg of binder per m². The thickness of this layer is approximately 1 cm after compaction.

This dual-layer procedure provides a better guarantee of waterproofing.

As a variant, it is also possible to produce the coating by spreading a single very thick layer of binder, the latter being produced in the middle of two layers of gravel, what is called the sandwich coating. We then proceed as follows: First spread on the ground a layer of gravel 6/10 then a layer of 2 liters in one go with binder NEOFLEX ^R then spread a layer of gravel 4/6.

This way of proceeding has the advantage of requiring only one spreading of binder instead of two and saves time.

b) Seat layer.

A 12 cm layer of 0/20 mm serious bitumen is produced, "optimized" with 5% bitumen (softening point 57 ° C) and applied hot to the layer obtained under a) serving as a "reservoir layer", which by fusion during compaction enriches the lower part of this base layer to make it richer in bitumen, therefore more enduring.

c) Surface layer.

A EURODUIT ^R surface layer is produced (according to French patent 89 09 893) and consisting of spreading 1 l of latex modified bitumen emulsion, at 62% concentration of binder (as a bonding coating) followed by spreading 27 kg of gravel 6/10 praline with 5% bitumen (thickness 12 mm).

d) Results.

• - couche d'accrochage, constituée d'un voile de bitume de 250 g/m²
• - couche d'assise en grave-bitume 0/20 mm, dosée à 4% de bitume (point de ramollissement Bille-Anneau 50-56°C), sur une épaisseur de 12 cm,
• - couche d'accrochage, voile de bitume de 300 g/m², et
• - couche de surface en béton bitumineux 0/10 mm dosé à 6% de bitume, sur 6 cm d'épaisseur.

We obtain a bituminous complex in three layers, with a total thickness of about 14 cm, which we compared with a usual structure of art, recommended in the manual of the French Administration for the reinforcement of a very damaged pavement. , performed as follows:

• - bonding layer, consisting of a bitumen veil of 250 g / m²
• - 0/20 mm gravel-bitumen seat layer, dosed with 4% bitumen (Ball-Ring softening point 50-56 ° C), on a thickness of 12 cm,
• - bonding layer, bitumen veil of 300 g / m², and
• - 0/10 mm bituminous concrete surface layer dosed with 6% bitumen, 6 cm thick.

The total thickness of this system is approximately 18 cm.

The differences between this prior system and the complex according to the invention are explained below:

WATERPROOFING LEVELS PREVIOUS SYSTEM

There is no level of impermeability provided specifically for this purpose and the impermeability of the system is given by the low porosity to water of the surface coating layer and the layer of severe bitumen.

It is slightly supplemented by the 2 bitumen sails, at 250 g / m² each, intended to bond the layers together.

SYSTEM EX. 1

• - une double couche de bitume sous la forme d'un enduit bicouche contenant 1,36 kg de liant par m² et ceci sous l'assise. Une partie de ce bitume va fondre et remonter enrichir le bas de la couche d'assise, et
• - une couche de bitume modifié 620 g/m² appliquée sous la couche de surface et destinée à assurer son rer son collage.

There are three levels of waterproofing:

• - a double layer of bitumen in the form of a two-layer coating containing 1.36 kg of binder per m² and this under the seat. Part of this bitumen will melt and rise to enrich the bottom of the seat layer, and
• - a layer of modified bitumen 620 g / m² applied under the surface layer and intended to ensure its bonding.

In addition, the serious base bitumen, which is richer in binder than that of the prior art, is clearly more compact and therefore less permeable to water.

COMPACITY BY LEVEL PREVIOUS SYSTEM

From top to bottom of the complex, the compactness continues to decrease from 93% at the top of the mix, up to 87% at the bottom of the bedding layer: only 50% of the total thickness exceeds 90% of coefficient filling.

From top to bottom the porosity to air and water therefore increases constantly.

SYSTEM EX. 1

• - en fond de couche où la compacité de l'enduit d'enrichissement bicouche atteint 99 ou 100%
• - sous la couche de surface où la compacité atteint 95%

From top to bottom of the complex, the average compactness is higher and exceeds 90% everywhere. There are two levels where this compactness exceeds 95%, or reaches 99%:

• - at the bottom of the layer where the compactness of the two-layer enrichment coating reaches 99 or 100%
• - under the surface layer where the compactness reaches 95%

From top to bottom, the water or air permeability is practically zero or very low, since there are two non-porous barriers to cross, including a double seal at the bottom of the seat layer.

BINDING CONTENT OF THE SEAT PREVIOUS SYSTEM

The bitumen content is 4% in the base and it is constant from top to bottom of the layer. At the support / seat interface and due to the attachment veil, the bitumen content is punctually very slightly increased.

SYSTEM EX. 1

The base is highly enriched at the bottom of the layer between approximately 10% of bitumen, the value of the "reservoir" coating and 5% which is its own bitumen content. This bituminous grade base layer considerably improves the fatigue resistance of the coating, precisely where the effects of fatigue are most felt as a result of the bending of the layer under rolling loads. ;

FATIGUE HOLD PREVIOUS SYSTEM

The weakest point of the structure from the fatigue point of view is the bottom of the seat. This is where the bending forces are highest and this is where the material is weakest (it is less compact than elsewhere and is not richer in bitumen than elsewhere).

SYSTEM EX. 1

The weakest point of the structure from the fatigue point of view becomes the top of the enriched zone. This is where the seat is the least compact and this is where it is the least rich in binder.
The enriched base layer and the "tank" coating become very resistant to fatigue because they are more and more rich in binder and also more and more compact. These two effects are the two most important parameters for a bituminous material to resist the effects of fatigue as best as possible. The bottom layer is therefore no longer the most vulnerable place.

Example 2 :

Application on a foundation of fine material such as fly ash, treated sand or silt.

• a) Préparation de surface d'une fondation de cendres volantes.
  Après répandage et compactage des cendres traitées (chaux + gypse) sur 34 cm, on répand à l'autogravillonneur 20 kg/m² de gravillons 6/20 mm pour effectuer un "cloutage" épais du sol. On arrose abondamment avec de l'eau puis on plante en force les gravillons à l'aide d'un compacteur jusqu'à ce qu'ils affleurent à peine en surface. On procède ensuite à un balayage pour éliminer les quelques gravillons mal fixés et la laitance. On obtient ainsi un cloutage sur environ 2 cm d'épaisseur.
• b) Couche d'enrichissement.
  On réalise un enduit bicouche de la même manière que dans l'exemple 1a).
• c) Couche d'assise.
  On réalise une couche d'assise de 10 cm d'épaisseur en grave bitume 0/14 mm optimisée à 5% en poids de bitume 40/50 dur (pénétrabilité 35/10 mm) ayant comme caractéristiques:
  • - compacite: environ 92%
  • - module E15: 11500 MPa
  • avec ε6 = 120 µdef.
• d) La couche de surface est réalisée comme dans l'ex. 1c).
  On obtient un complexe bitumineux routier qui permet, moyennant une préparation de surface par cloutage épais, un emploi plus systématique de matériaux pauvres, comme les cendres volantes.

On this type of foundation, the most important problem to solve is the bonded assembly between bituminous materials and a foundation made of fine or even powdery materials. Indeed the latter often constitute a dust barrier which prevents any lasting sticking. It is therefore necessary to proceed with the thick studding beforehand of the foundation with 10 to 30 kg / m² of gravel.

• a) Surface preparation of a fly ash foundation.
  After spreading and compacting the treated ash (lime + gypsum) over 34 cm, 20 kg / m² of 6/20 mm gravel is spread to the autograveller to make a thick "nailing" of the soil. We water abundantly with water and then we force plant the gravel with a compactor until they barely come to the surface. A sweep is then carried out to remove the few loose gravel and the milt. One thus obtains a studding on approximately 2 cm of thickness.
• b) Enrichment layer.
  A two-layer coating is produced in the same manner as in Example 1a).
• c) Seat layer.
  A 10 cm thick base layer is made of 0/14 mm serious bitumen optimized to 5% by weight of 40/50 hard bitumen (35/10 mm penetrability) having the following characteristics:
  • - compactness: around 92%
  • - E15 module: 11500 MPa
  • with ε6 = 120 µdef.
• d) The surface layer is made as in the ex. 1 C).
  A bituminous road complex is obtained which allows, by means of a surface preparation by thick nailing, a more systematic use of poor materials, such as fly ash.

Example 3 :

• a) Traitement de la fondation
  On traite la craie avec 6% d'un liant hydraulique spécial contenant 10% de sulfate de calcium, sous la forme de gypse, et 5% de clinker, le complément à 100% étant constitué de laitier de haut fourneau finement moulu, l'ensemble du liant ayant une surface spécifique Blaine de 4500 cm² par gramme, (produit décrit dans la demande de brevet français déposée ce même jour et intitulée "Liant hydraulique de type ciment destiné au traitement des matériaux calcaires tels que la craie et son procédé d'utilisation".
• b) Application du complexe bitumineux
  Ici le complexe bitumineux selon l'invention s'applique tel quel étant donné que la couche d'enrichissement colle immédiatement et correctement sur la craie traitée.

Application on a chalk foundation treated with cement.

• a) Treatment of the foundation
  The chalk is treated with 6% of a special hydraulic binder containing 10% of calcium sulphate, in the form of gypsum, and 5% of clinker, the complement to 100% consisting of finely ground blast furnace slag, the set of binder having a Blaine specific surface of 4500 cm² per gram, (product described in the French patent application filed the same day and entitled "Hydraulic binder of cement type intended for the treatment of calcareous materials such as chalk and its process of use".
• b) Application of the bituminous complex
  Here the bituminous complex according to the invention is applied as it is, since the enrichment layer immediately and correctly sticks to the treated chalk.

Under these conditions, the nailing operation described in Example 2a) is not necessary, although it remains advisable. All the layers of the complex are produced in the same way as in Example 2.

Example 4 :

Application in the repair of coatings on a bridge deck:

The old coating is removed and the surfaces are cleaned (dust removal).

The enrichment coating is produced as described in Example 1a.

Then apply a layer of seat intended mainly to restore a flat surface to the apron and to allow the comfortable passage of cars. This base layer is a 0/14 mix coated with 5.4% bitumen and has an average thickness of 7 cm (4 to 10 cm depending on the location since it is mainly used for reprofiling).

On this foundation we apply a molten waterproofing bitumen, in a regular layer and without spraying , layer which is then sanded to avoid sticking of the machines.

The surface layer is then applied as in Example 1c but without spreading the binder layer which already exists.

In total, an economic complex is obtained, with three levels of waterproofing and not requiring the intervention of specific equipment and know-how to achieve the watertightness of the structure's deck.

Claims (11)

Method for building a bituminous road complex on a support floor, comprising the production of at least one base or base layer and / or a wearing course, with possible interposition of a bonding layer, characterized in that there is applied to the support, before the seat layer, an enrichment layer by binding from the bottom of the seat, comprising at least one layer of aggregates and at least one layer of binder dosed at more 800 g / m². Method according to claim 1, characterized in that the base layer comprises between 4.5 and 5.5% by weight of bitumen. Method according to claim 2, characterized in that the bitumen has a ball and ring softening point between 52 and 65 ° C. Method according to one of claims 1 to 3, characterized in that the seat layer has a thickness of 7 to 25 cm representing more than 80% of the entire thickness of the complex. Method according to any one of Claims 1 to 4, characterized in that the wearing course has a thickness of 1 to 4 cm. Process according to any one of Claims 1 to 5, characterized in that the enrichment layer is produced with 1.2 to 3 kg / m² of binder. Method according to claim 6, characterized in that the enrichment layer is produced by spreading n layers of binder and n or n + 1 layers of gravel with a granularity of 4/6 or 6/10 mm inserted, n being able to take the values 1 or 2. Method according to any one of Claims 1 to 7, characterized in that the support is consisting of an old road to be reinforced. Process according to any one of Claims 1 to 7, characterized in that the support consists of a foundation of treated fine materials, and subjected to a thick studding with 10 to 30 kg / m² of gravel followed by watering and compacting . Method according to any one of Claims 1 to 7, characterized in that the support consists of chalk treated with a hydraulic binder. Method according to any one of claims 1 to 7, characterized in that the support consists of a work of art.